1. Field of Invention
The invention relates to smoke detectors having dark chambers and more specifically to structure for blocking light from the chamber and controlling light reflections within the chamber without significantly impeding the circulation of airborne particles such as smoke.
2. Description of the Prior Art
Prior art smoke detectors typically include a dark chamber through which airborne particles of smoke are free to circulate. An emitter within the chamber directs infrared radiation along a defined path, while a photoelectric sensor, positioned out of the path, is aimed to view the chamber and any radiation scattered by circulating smoke. When the sensor detects a level of scattering above a predetermined threshold, it issues an alarm signal.
The dark chamber usually has a cylindrical configuration including top and bottom walls sometimes separated by a labyrinth structure that blocks light from the chamber but not smoke. Kawai U.S. Pat. No. 4,851,819, issued on Jul. 25, 1989, is an example including a plurality of "L-shaped" wall elements that also suppress internal scattering from the surfaces of the chamber.